The present invention is related to a process for preparing silica pigment, and in particular to a process for preparing silica pigment by mixing sea water and an aqueous solution of sodium silicate.
U.S. Pat. No. 3,202,525 discloses a process for forming silica pigment from an aqueous medium containing sodium silicate, in which sea water is added to the aqueous medium in the portion of from about one-half liter to about fifteen liters per mole of alkalinity, calculated as Na.sub.2 O, of the sodium silicate during the addition of an acidulating agent. According to the teaching of this prior art the acidulating agent is indispensable for forming the silica pigment as a precipitate. Moreover, the effect of the mixing ratio of sea water and sodium silicate on the yield of the silica pigment has not been discussed in U.S. Pat. No. 3,202,525, in Example II of which the mixing ratio of sea water and sodium silicate was about 26.4 by weight.